A consistent thermodynamic scheme for the quasiparticle models of the quark-gluon plasma

by Prof. Guruprasad Kadam (JIIT, Noida)

Thursday 15 Jan 2026, 14:30 → 15:30 Asia/Kolkata

A-304 and On Zoom

Quasiparticle models provide an effective description of the quark–gluon plasma by encoding interaction effects into medium-dependent quasiparticle parameters and treating the gas as an ideal one. However, when the quasiparticle spectrum depends explicitly on temperature and chemical potential, the formulation of thermodynamics becomes subtle, particularly with respect to the interpretation of entropy and the treatment of rearrangement contributions. In this work, we propose a consistent thermodynamic scheme in which the entropy is fixed a priori to retain the ideal-gas functional form associated with quasiparticle excitation microstates. Starting from exact equilibrium identities, we show that the explicit temperature dependence of the spectrum generates a rearrangement contribution that cannot be consistently absorbed into the entropy. We therefore introduce an explicit reversible energy term, $Q_\beta$, in the first law of thermodynamics, which accounts for the energy required to continuously re-dress quasiparticles as the medium evolves. The associated background contribution $\Phi(T,\mu)$ is identified as the integrated rearrangement energy density and enters the equation of state in a manner analogous to a bag term, while possessing a distinct physical interpretation as a genuine thermodynamic energy-exchange channel. Standard Legendre relations are preserved by construction, and the formulation admits a transparent extension to finite chemical potential. The present approach clarifies the thermodynamic role of medium-dependent quasiparticle parameters and provides a conceptually clear alternative to existing quasiparticle models.